Underquoting is rife in Melbourne, according to a group of prominent real estate agents and buyers' advocates, who say the deceptive tactic leaves thousands of prospective buyers out of pocket each week and brings the industry into disrepute.

The group launched a petition on change.org on Thursday calling for the state government to compel agents to publish vendors' reserve prices at the start of sales campaigns to stamp out the practice.

They said agents ignored guidelines for price advertising and underquoting and that moves to crack down on the ingrained practice had failed.

'Many agents are trained with scripted vocabularies to disguise the figure they know their vendors want.' Photo: Louise Kennerley

This results in bait pricing, the authors said, and leads to prospective buyers spending money on lawyers' fees, building and pest inspections, before being priced out of a market they were never in.

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''Price representations by estate agents are frequently significantly below a price a selling agent knows a property is likely to sell for, and well below what agents know their vendors will accept,'' the petition said.

Co-author John Keating, a former chairman of the Real Estate Institute of Victoria ethics committee whose membership was temporarily suspended in 2009 after speaking out about underquoting, said the tactic was used in auctions and private sales mainly in metropolitan Melbourne.

The ploy, which increasingly involves agents holding back a guide price and using terms such as ''no price displayed'' or ''price on application'' when promoting property, was most prevalent in high-volume-auction suburbs in Melbourne's inner east and bayside areas, he said.

''Many agents are trained with scripted vocabularies to disguise the figure they know their vendors want,'' he said.

''It's across all price ranges, from the lower end of the market up to $5 million properties.''

Mr Keating said properties routinely sold for $100,000 above an agent's highest estimate, while more expensive properties - in areas such as Camberwell, Kew, Brighton and Albert Park - were selling for more than $500,000 above estimates.

Mr Keating cited a recent example where an agent gave a potential buyer a guide price that was about $400,000 less than the reserve.

Consumer Affairs received 745 complaints about real estate agents last year, including 75 that related to underquoting, most of which were not proved.

Director Claire Noone said requiring the auction reserve price to be disclosed could ''distort the market and jeopardise the auction selling process''. Dr Noone said it was an offence to misrepresent the price of a house but there was no law requiring the estimated selling price and the reserve to be the same.